Heat-enduring metal



NOAK VICTOR HYBINETTE, OF WILMINGTON, DELAWARE.

EEAT-ENDUBING METAL.

Ho Drawing. Application filed July 12,

This invention relates to heat-enduring metals, and particularly to alloys which resist to a material extent the effect of oxygen and other deteriorating influences under high temperatures, particularly the influence of alkali. Such alloys have numerous uses in the arts and are desirable especially where conditions exist which tend .to cause the rapid destruction ofmetals heretofore avail- 1o able for such purposes.

The basis of the invention is an alloy .of iron, nickel and chromium. Alloys of-these elements have been known heretofore and are used for various purposes. So far as they meet the conditions under which they are used the alloys are satisfactory but they are useless in many cases because their endurance to oxidation, and particularly to the influence of alkalies, is relatively limited. I have discovered that alloys containing these elements in certain limited proportions are much more resistant to deterioration at high temperatures than alloys heretofore known, particularly deterioration by alkali at high temperatures, and that an alloy containing these elements in proportions corresponding to the atomic weights of the elements has the highest degree of endurance under adverse conditions. Such an alloy 30, which I have found valuable consists of 33 per cent iron, 36 per cent nickel, and 31 per cent chromium, approximately, and is unaffected to any material extent by exposure to air or furnace gases and alkali salts at temperatures as hi h as 2100 F. Any oxidation resulting rom such exposure involves the formation merely of a skin coating of oxide which is tough and adherent and protects the underlying metal from fur- 40 ther oxidation. This resistivity to alkali becomes noticeable with 18% nickel and 28% chromium and the remainder mainly iron, and shows a pronounced diminution with over 40% nickel, over 40% chromium and less than 20% iron.

I have studied particularly the effect of alkalies upon such alloys as well as upon alloys of iron, nickel and chromium, such as have been known heretofore. The deterioration of the heretofore known alloys in the presence of alkalies has been observed andl ascribed generally to causes other than the presence of alkali. I find, however, that the alkali is almost always present in sufiicient quantity to be of considerable importance and attacks the metal, combines therewith 1924. Serial No. 725,692.

and acts apparently as a catalyzer so that oxidatlon is rapid and destruction of the metal follows quickly. The effect of the alkali does not depend upon direct contact thereof with the metal although deterioration is more rapid where the alkali is applied ing 35 per cent of nickel, 20 per cent of chromium, and 45 per cent of iron, or an alloy containing 30% chromium with little or no nickel and the'rest iron, will, when heated electrically to about 2000 F. in the presence of air, lose approximately one milligram of metal per square centimeter in twenty-four hours. If a small quantity of soda ash is applied to the surface of these metals in the proportion of five tenths of a milligram per square centimeter, the oxidation is increased to from 10 to 100 milligrams per square centimeter. The mere introduction of a similar amount of soda ash in the furnace but not in contact with the metal results in approximately the same rate of acceleration of the oxidation by the vapors acting on the alloy.

On the other hand, the new alloy which I have herein described can be heated almost indefinitely to the temperature and under the conditions mentioned without material loss by oxidation. Even in the presence of sodlum or other alkalies there is no material amount of oxidation or other destruction of the metal. The alloy is, therefore, particularly useful in connection with operations requiring prolonged heating in the presence of oxidizing or furnace gases, and especially where alkalies contact with the metal or are present in the atmosphere to which it is subjected.

The atomic proportions mentioned are not absolutely essential to the accomplishment of the purpose of the invention and can be varied to a limited extent depending upon the particular use for which the alloy is intended. The physical characteristics of the metal will vary greatly with the nickel content but its endurance of the deteriorating influences of alkali salts does not materially change if the proportions of the elements are main tained within the limits hereinafter mentioned. The nickel content of the alloy can be reduced to approximately 20 per cent without out impairing its endurance to any (.(iOllHlVG degree, and l have found that an alloy containing 50 per cent of iron, 20 per cent of nickel and 30 per cent of chromium has marked endurance in the presence of alkalies and also the highest physical strength at high temperatures. It will withstand the effect of an oxidizing atmosphere at a temperature of about 2100" F. for an almost indefinite time.

The alloy with about 35% nickel has practically the highest resistivity to alkali but is not so strong. The chromium content can be varied from about 28 to 40%, but in general there is little gained by using more than about 30 to 32 per cent.

My invention primarily consists, therefore, in an alloy of iron, nickel and chromium, in which the chromium content is always'approximately 30 per cent and in which the nickel varies from 18 to 40 per cent with cor responding proportions of iron. Such an al loy meets all of the requirements for many uses in which the alloy is subjected to oxidation and other deteriorating influences. Its

characteristics can be modified, however, without destroying the properties mentioned to make it suitable for other purposes.

The alloys described are somewhat hard and brittle and cannot be rolled and drawn satisfactorily. It is possible, however, to modify the hardness of the metal by additions of cobalt or copper. Cobalt is enerally assumed to impart to such alloys the same properties as nickel does, but. this is not true in the present case. For example, the addition of from one to 10 per cent of cobalt softens the alloy appreciably and imparts a finely grained structure. Copper is usually considered to be detrimental to alloys containing chromium and nickel, but the alloys described can be modified by additions of from five tenths to five per cent of copper without reducing the enduring properties. The copper serves the same purpose as cobalt in softening the metal and is a cheaper agent for that purpose.

Where great mechanical strength is requisite the addition of copper and cobalt is to be avoided as an amount in excess of one tenth of one per cent of copper reduces the strength materially. As much as 3 per cent of cobalt can be used, without reducing the strength materially.

The alloys, either with or without copper or cobalt, can be modified bythe presence of varying proportions of carbon and silicon. The presence of the usual amounts of these elements in the alloys does not affect their properties materially forcertain purposes. For rolling and drawing, however, silicon and carbon are undesirable and should be reduced to the lowest practicable proportions. Both of these elements tend-to make the metal hard and brittle.

As specific examples of the preferred compositions an alloy for castings having the highest possible endurance to the elfect of oxygen and alkali should contain, in addition to iron, the following elements in approximately the proportions mentioned:

In addition the metal may contain copper 1% or cobalt 1 to 10%. The addition of the latter elements is optional because these elements do not influence the endurance of the metal and they are added only to ensure against brittleness. A reduction in the amount of carbon, silicon and aluminum will also soften the metal. The chromium and nickel content can be increased to approximately 40 per cent of each before a very decided decrease in the resistivity of the metal to corrosion is noticeable. However, such increase is not desirable as it increases the cost of the alloy without corresponding advantages.

This alloy has the peculiar property of forming under oxidizing conditions in the presence of alkali a tough adherent surface of oxide having the consistency of graphite. The oxide coating adheres to the metal in spite of repeated heating and consequently protects the surface of the metal from the further action of oxygen or other deteriorating elements. Receptacles made of this alloy and provided with such a surface coating are useful for many chemical purposes in addition to handling of alkali compounds, such, for example, as the melting of aluminum. In

the latter use care should be taken that the Chromium between 28 and 32%, preferably 3 0 Nickel between 18 and 22%, preferably 20 Carbon between 1 and 12%, Preferably 1. 5% Silicon to 2%, Preferably 1 Aluminum 1 to 2%, preferably 5% Manganese 0 to 5%, preferably 5% It is understood that in this and the composition previously described the amount of iron is proportionate to complete the composition.

For heat-treatment containers the composition last described may be used preferably with the addition of .5% to 2% of copper or upward to 5% of cobalt. For cyanide pots and salt baths the nickel should be increased advantageously to from 30 to per cent as the highest resistivity to the efl'ect of alkali is obtained in an alloy having such proportions of the elements mentioned,

From the foregoing it will be observed that the proportion of nickel but not of chromium may be varied within a relatively wide range so as 'to obtain the most desired properties of the alloy in each particular case. My invention resides, therefore, in the discovery of the peculiar characteristics of alloys of iron, nickel and chromium within the specified range of proportions and includes such alloys with an addition of elements which modify the properties of the alloys without destroying the quality of endurance to deteriorating conditions at high temperatures. Thus, while the maximum endurance is obtained with an alloy containing approximately 35 per cent of nickel, the greatest mechanical strength with a fair degree of endurance is obtained with an alloy containing approximately 20 per cent of nickel. Also while these alloys are not suitable for operations requiring malleability, a certain degree of toughness can be acquired by the addition of cobalt or copper or both without losing the advantages of the harder alloys with respect to deterioration.

I have mentioned a few of the possible uses of the alloy and the particular compositions which are best adapted for employment in connection therewlth. The effect of the several constituents has been described in more or less detailin order that the possibility of varying the properties of the alloy by increasing or diminishing the proportions of the added constituents may be clear. Various changes maybe made, therefore, in the details of the invention, particularly with respect to the proportions of added constitu- 2. A heat resisting structure adapted to withstand the action of alkali compounds at high temperatures, such structure being made of an alloy containing approximately 28 to 40% of chromium and 18 to 40% of nickel, the balance consisting principally of non.

3. A heat resisting structure adapted to withstand the action of alkali compounds at high temperatures, such structure being made of an alloy containing approximately 28 to 32% of chromium, about 18 to 40% of nickel,

and the balance principally of iron.

4. A heat resisting structure adapted to withstand the action of alkali compounds at high temperatures, such structure being made of an alloy containin approximately 28 to 40% of chromium and 18 to 40% of nickel, the balance consisting principally of iron, said structure having a tough adherent oxidized coating.

5. A heat resisting structure adapted to withstand the action of alkali compounds at high temperature, said structure being made of an alloy consisting mainly of chromium and iron, with a chromium content of from 28 to 40% suflicient to give heatresistance at or about 2000 F. and said alloy containing from -18 to 40% of nickel and being thereby made heat resistant in the compounds.

In testimon whereof I afiix my signature.

NOAlK VICTOR HYBINETTE.

presence of alkali 

